Sorry, no formal defiinition of "mad". I think the devs would know. IMHO, it's not good enough if the track editor is flexible, versatile, complete, etc.
It needs to be "Huh ?".
I already have MotorStorm as a mature standin for Mario Kart (I know, no weapons... but the off-road tracks and aggressive AI grab my attention). ModNation Racer needs to be more different or addictive if it wants to stand out.
You mad.